1. Technical Field
This application is related to systems for authenticating signals, and more particularly to systems for authenticating a radio-frequency identification tag.
2. Description of Related Technology
With the ubiquity of RFID tags in modern life, concerns about the security of RFID have arisen. Cloning of RFID tags in devices such as car keys or ID badges can lead to security breaches, as discussed in A. Juels, “Rfid security and privacy: A research survey”, EE J. Selected Areas in Communication, Vol. 24, No. 2), pp. 381-395, February 2006. For example, as described in S. Bono and M. Green, “Security analysis of a cryptographically-enabled rfid device”, 14th USENIX Security Symposium, pages 1-16, 2005, researchers at Johns Hopkins University and RSA Laboratories were able to apply reverse engineering to simulate an ignition key for their own car and to clone a Speedpass® RFID token for purchasing gasoline.
Some proposed fixes to RFID security involve stronger encryption of the RFID code, or restricting physical access to reading the RFID device. However, stronger encryption can be too expensive to apply to inexpensive RFID tags. Devices such as ID badges are not easily restricted from being read by RFID readers.
In the electronic warfare arena, specific emitter identification techniques have been developed at the Naval Research Laboratory to catalog radar transmitters, and to later intercept a radar signal and uniquely identify the radar transmitter that is the source of that signal.
In Radio Science, Vol. 36, No. 4, pp. 585-597, July-August 2001, K. J. Ellis and N. Serinken discuss extracting features from the transient start up phase of a VHF radio transmission, and using those characteristics to unambiguously identify an individual transmitter.
S. C. G. Periaswamy, D. R. Thompson, J. Di, “Fingerprinting RFID Tags”, IEEE Transactions on Dependable and Secure Computing, 21 Oct. 2010, IEEE computer Society Digital Library, <http://doi.ieeecomputersociety.org/10.1109/TDSC.2010.56>, discusses using a tag's minimum power responses at multiple frequencies as a uniquely identifying fingerprint of the tag.
N. Saparkhojayev and D. R. Thompson, in “Matching Electronic Fingerprints of RFID Tags using the Hotelling's Algorithm”, IEEE Sensors Applications Symposium, New Orleans, La., Feb. 17-19, 2009, propose creating an electronic fingerprint of a tag, with different features such as amplitude, frequency, phase, and timing, and using the Hotelling's T2 algorithm to compare a tag's fingerprint with a database of tag fingerprints.
D. Zanetti, B. Danev, and S. Capkun, in “Physical-layer identification of UHF RFID Tags”, Proceedings of the Sixteenth Annual International Conference on Mobile Computing and Networking, MobiCom '10 on Sep. 20-24, 2010 in Chicago, Ill., ACM, pp. 353-364, evaluate using measured time domain features and spectral domain features of passive UHF RFID tag preambles for classifying and identifying RFID tags.
U.S. Patent Publication No. 2006/0181394 to Clarke describes a method for comparing an RFID tag fingerprint to an expected RF fingerprint, with the fingerprint including measurements of signal amplitude, phase, and frequency. Other U.S. patents and patent applications in this area include U.S. Patent Application Publication No. 20030234718 to Fujisawa, U.S. Pat. No. 5,420,910 to Rudokas, U.S. Pat. No. 6,229,445 to Wack, U.S. Patent Application Publication No. 20080079540 to Aull et al., U.S. Pat. No. 5,420,910 to Rudokas et al., and U.S. Patent Application Publication No. 20090201133 to Bruns.